Radar detectors have been known for some considerable time. Police radar devices that are used in the detection and measuring the speed of moving vehicles, and also intrusion and zone security devices that are used on buildings, operate in various frequency bands, often depending on the country in which they are operating. For example, in North America it is common for police devices to operate in the X-band, at 10.525 gHz, and the K-band at 24.150 gHz. In Europe, however, police devices may operate in very different bands.
Moreover, because of the changes in the manner of use of police radar--e.g., in a pulsed manner or aimed crosswise to the traffic flow, it has become more necessary to provide radar detectors with increased sensitivity.
U.S. Pat. No. 4,630,054 issued Dec. 16, 1986 to Martinson, disclosed a radar detection and signal processing circuit for frequencies in both the X- and K-bands, and which also provides for inhibited sensitivity in other bands. This is achieved, for example, by mixing the signals received by the detector with a local oscillator output of such a frequency which, when its first or second harmonic is mixed with an X-band or K-band signal respectively, the resultant produces a particular intermediate frequency signal. This intermediate frequency signal may be mixed with a signal from a swept frequency oscillator, and thence through a band pass filter and other signal processing circuitry, to actuate the alarm.
Since signals other than from the X-band and the K-band will not mix with the local oscillator output to produce an intermediate signal of the required frequency, these other signals are effectively ignored by the device.
Unfortunately, it has not been possible to use this system effectively for more than two or possibly three frequency bands, since the strength of the intermediate signal diminishes with each higher harmonic of the local oscillator utilised. Moreover, even the signal strength for the K-band using the second harmonic of the local oscillator is diminished with respect to that for the X-band.
It is an aim of the present invention to provide a radar detector that can be used for a variety of frequency bands to provide a substantially uniform signal to actuate the alarm. It is envisaged that the number of frequency bands coverable will usually be more than two.